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Revenue Recognition - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Mar. 31, 2024
Contract With Customer Assets And Liabilities [Line Items]
Receivables billed but not paid under retainage provisions in its customer contracts	$ 1,618	$ 1,875
Revenue remaining unsatisfied performance obligations amount	384,701
Customer Deposit [Member]
Contract With Customer Assets And Liabilities [Line Items]
Contract liabilities	$ 7,122	$ 21,426

X

- Definition

Contract with customer assets and liabilities.

+ References

No definition available.

+ Details

Name:	ghm_ContractWithCustomerAssetsAndLiabilitiesLineItems
Namespace Prefix:	ghm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The amount of obligation to transfer good or service to customer for which consideration is receivable.

+ References

No definition available.

+ Details

Name:	ghm_ContractWithCustomerLiabilityConsiderationReceivable
Namespace Prefix:	ghm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract.

+ References

No definition available.

+ Details

Name:	ghm_ContractWithCustomerReceivablesBilledButNotPaidUnderRetainage
Namespace Prefix:	ghm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-SubTopic 10
-Topic 606
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-13

+ Details

Name:	us-gaap_RevenueRemainingPerformanceObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=ghm_CustomerDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: